1. Field of the Invention
The invention relates to an apparatus and a method for diagnosing a system malfunction in a sliding mode control system, for example, of a type used for the feedback control in a valve timing control apparatus of an internal combustion engine.
As a valve timing control apparatus constituted to successively and variably change the opening and closing timing of intake and exhaust valves by changing a rotation phase of a camshaft relative to a crankshaft, a vane type valve timing controlling apparatus as disclosed in Japanese Unexamined Patent Publication 10-141022 is conventionally known.
In the conventional valve timing apparatus mentioned above, when a rotation phase can not be controlled to a target value, the result is a deterioration of the operating performance of an engine. Therefore, the conventional valve timing apparatus is provided with a diagnosis apparatus for diagnosing an abnormality in control function of the rotation phase. When the occurrence of an abnormality is diagnosed, a fail-safe process is performed.
The above diagnosis apparatus judges whether there is an abnormality, for example, based on control errors of a time when a predetermined period of time has elapsed after a target value of the rotation phase has changed.
However, in the above valve timing apparatus, sometimes there occurs a stationary deviation, since it is difficult to control an actual rotation phase (valve timing) to a target value with accuracy due to fluctuation in angle velocity of the camshaft and fluctuation in oil temperature and oil pressure.
Accordingly, in view of prevention of misdiagnosis, it is needed to set the above conventional diagnosis to judge an abnormality when relatively large control errors occur, and time is required to adapt the judgment level.
Further, in the conventional feedback control by proportional, integral and differential operations, it is desirable that a feedback gain is set to be variable in accordance with the oil temperature and the oil pressure, to improve response characteristic. However, since gain matching is not easily performed, consideration is made to shift to a sliding mode control that is hardly influenced by disturbance.
2. Summary of the Invention
In view of the foregoing, the present invention has been accomplished and has an object of providing an apparatus and a method for diagnosing a system abnormality with high accuracy and with a little adaptation time in a feedback control system using a sliding mode control.
For achieving the above object, with the present invention, in a sliding mode control system where an operation amount is calculated based on a non-linear term calculated corresponding to a switching function and a linear term, to feedback control a control object amount to a target value, the constitution is such that an abnormality judgment signal of the sliding mode control system is output based on a variation in the operation amount within a predetermined time from when a predetermined period of time has elapsed after the target value has changed.
More specifically, when the operation amount by the non-linear term does not change within a predetermined time from when a predetermined period of time has elapsed after the target value has changed, an abnormality judgment signal of the sliding mode control system is output.
When the system is normal, since the operation amount by the non-linear term performs a switching function when the control object amount is approaching the target value after changed, the presence of system abnormality is judged based on whether or not the switching function occurs.
The switching function of the operation amount by the non-linear term may be judged based on a change of code of the operation amount by the above non-linear term.
In the case the linear term is consisted of an operation amount in proportion to a control deviation and an operation amount in proportion to a change velocity of the control object amount, the constitution may be such that when the operation amount in proportion to the change velocity of the control object amount does not change within a predetermined time from when a predetermined period of time has elapsed after the target value has changed, an abnormality judgment signal the sliding mode control system is output.
When the system is normal, since the operation amount by the non-linear term performs a switching function when the control object amount is approaching the target value after changed, and the control object amount changes with such switching function, so that the above change velocity changes, the abnormality can be judged based on the change of the operation amount in proportion to the change velocity.
The diagnosis apparatus and method according to the present invention, can be applied to a system for feedback controlling a valve timing in a variable valve timing apparatus in an internal combustion engine to a target value using a sliding mode control.